High powered lasers used for welding or drilling are well known in the art. Typically, these lasers, such as the 14 kilowatt model laser marketed by the Industrial Laser Division of United Technologies Corporation, are of the transverse electrode, convective flow type. In these lasers, large volumes of carbon dioxide gas or an equivalent gaseous lasing medium are flowed through a region of opposed electrodes. A gas discharge is created between the electrodes, creating the population inversion that is needed to generate a high powered, coherent beam.
Adjoint feedback has been found to be a way of controlling the operation of a laser. Adjoint feedback consists of taking a portion of the output of a laser and retroreflecting it back into the adjoint mode (the converging wave) of the resonator or, in the case of coupling, injecting it into the adjoint mode of another laser. The advantage of using an adjoint feedback beam is that it is a small low power beam which is not part of the main resonator. Optics in the adjoint feedback beam can be readily changed or rotated. A laser embodying the same is disclosed and claimed in a commonly owned, co-pending U.S. patent application entitled "Optically Pulsed Laser", Ser. No. 781,430, pending incorporated herein by reference.
Pulsing of high power industrial lasers has a number of potential applications, such as paint stripping. The potential for suppression of the plasma which forms on a metal target also may give improved welding, hole drilling, and cutting performance. Also, the higher peak power which is potentially achievable with pulsed operation may allow welding and cutting of metals which are now difficult, such as aluminum and copper. A technique for Q-switching using adjoint feedback beam with an unstable resonator is disclosed and claimed in the copending, commonly owned U.S. patent application entitled "Optically Pulsed Laser", filed on even date and incorporated herein by reference.
The useful power range for these lasers is limited by the power limit of the chopper or modulator. The power limits constraining modulators are more severe. However, modulators offer many advantages, including more abrupt opening and closing times, higher repetition rates, and the potential for tailoring optical pulse shapes. Commercially available modulators for CO.sub.2 laser radiation are limited to optical beams of about 100 W of average power.
It would be advantageous to have a high powered laser of the aforementioned type characterized by adjoint feedback that is capable of operating at very high power. The present invention is drawn towards such a laser.